All main effects, with the exception of hearing level blocks, were
significant, in addition to several interactions. These are discussed
in detail and depicted graphically. One fundamental finding was that
none of the hearing protection devices degraded speech discrimination
(in comparison to an unoccluded condition) in the 83 dBA ambient noise
level. In fact, the most protective HPD significantly enhanced speech
discrimination in the high noise level. In the low ambient noise
level, there was some reduction in discrimination due to the wearing of
an HPD, but this effect is not of concern because HPDs are not needed
at low ambient levels for protection purposes. From the results, it
appears that properly selected HPDs can be expected to at least maintain
speech discrimination levels (equivalent to unoccluded levels) in
moderately-high intensity industrial noises of varied spectral
characteristics.